Local area network (LAN) is the name which has been given to the equipment and protocols permitting users of computers within an organization to attach to a communication network which allows the users to share information and resources. Not only are those in nearby physical locations able to share resources such as printers and plotters and computer programs and files in memory, but with remote bridges, stations anywhere can join the network via telephone lines if they have proper access authorization. The IEEE has been developing a standard for LAN so that the equipment of various manufacturers will be interoperable. Historically, the field had developed independently for several years prior to the adoption of a standard so that a de facto standard had developed before the IEEE had proposed their standard. Accordingly, four different standards were developed for networks, each having a different method of approaching network problems; the main problem is how to recognize and deal with data collisions among the sharing nodes on the network. In this invention we are only concerned with the IEEE Std 802.3. (This standard was intended to be compatible with the network of the Xerox Company called EtherNet.) The 802.3 specification deals with data packet formation issues and collision avoidance protocol which has become known by the mnemonic CSMA/CD for Carrier-Sense Multiple Access with Collision Detection. In accordance with this scheme each station senses if there has been a collision and if so each station involved waits a random time before resending its message and uses certain sophisticated procedures to avoid multiple collisions. The IEEE 802.3 was originally developed for use with a thick coax cable bus network and called the specification for use with this cable 10Base5 because it described a baseband coaxial cable which could transmit data at 10 Mbs over a maximum distance of 500 meters between stations. Subsequently, a thinner baseband coax bus cable became used because it was less expensive and it was called 10Base2. It is specified for the same 10 Mbs but only over maximum 200 meters. Another network configuration is configured as a distributed star using inexpensive twisted-pair wire and is called 10Base-T. Again, it will operate at the same 10 Mbs but at a still less maximum distance of 100 meters. 10Base-T has a hub which can recognize when a station is faulty and can bypass that work station so that the entire network is not disrupted.
With respect to FIG. 1, the nomenclature for the physical interconnection is illustrated between a computer 2 and a Network 6. The Computer 2 contains a Local Area Network Controller Board 1 having Port 1 and Port 2. Port 1 is shown connected to coax media 7 for 10Base2 or 10Base5. Port 2 is shown connected to a pair of twisted pair cables 8 and 9.
The IEEE 802.3 standard requires that the physical media, either coax or twisted wire are connected to a Media Attachment Unit (MAU) via connector 5 and 10 respectively. The connectors are called Medium-Dependent Interface (MDI). The IEEE Specification requires for the coax media, because it is required to exhibit high voltage isolation, that the MAU 4 be connected to another unit called an Attachment Unit Interface (AUI) 3. The IEEE specification does not require a separate AUI between the LAN Controller Board 1 and the twisted pair 10Base-T MAU 11. In existing LAN systems it is known to separate units interconnected as shown in FIG. 1 or to combine the MAU and AUI units into the computer so that it is convenient for the user to simply connect their cables into the connectors (MDI) 5 and 10 on the back of the LAN Controller Board 1.
With reference to FIG. 2A and FIG. 2B, prior integrated circuit network controller chips 20 and 26 have been mounted and connected differently to the coax ports for an AUI and the 10Base-T ports. These differences have caused certain ambiguities and problems. Since both 10Base2, 10Base5 and 10Base-T employ the same 802.3 collision detection protocols, it has been the practice to employ a single Network Controller Integrated Circuit 20 and 26 on a Network Controller Board and to require the user to take certain steps when it is determined which type of media is going to be used. As illustrated in connection with FIG. 2A, if the user is going to connect to coax which are to be accessed via the AUI Port 23, then the switch 21 must be activated to apply a high on the 10Base-T MAU 22 disable circuit to disconnect the 10Base-T port. However, if the 10Base-T port 24 is selected by de-energizing switch 21, if through error any signals are subsequently introduced from coax through the AUI port 23 they will contend with the 10Base-T data in an illegal manner. Accordingly, in the configuration of FIG. 2A, the AUI port 23 must be left open or problems can occur.
In reference to FIG. 2B, the selection between the coax port 23' and the 10Base-T port 24' is taken care of by the use of a jumper block 27. When the user makes the decision as to which media his system will be connected to, it is necessary for the user to install or remove the jumper across the jumper block 27 to make the required port interconnections to the chip and to open the other port.
This problem has made it more difficult for users to connect their systems and for integrated circuit designers. Also, it would be more convenient to include the MAU circuitry for the 10Base-T into the integrated circuit but because of the user selection requirement, this integration has not been able to be accomplished before my invention.